Broken 520 Bridge Cable Under Repair, State Investigating

State transportation officials are investigating why a 550-foot steel cable that anchors the State Route 520 bridge to Lake Washington broke.

The damage was discovered on the westernmost anchor on the north side of the bridge on Tuesday, and crews are expected to finish replacing the broken cable by Saturday at the latest, according to Dave McCormick, WSDOT assistant regional administrator. There will be no impact to traffic for this repair, he said.

The cable was completely severed, and it was unlikely to have been caused by weather, McCormick said. It is unusual to have this type of damage to the bridge, and the cause is suspected to be a collision, he said.

"It was a hard impact," he said. "It depends on where and exactly how, but something big hit it. Or at least a large impact hit it. If it wasn't a large thing, it was certainly a strong force." 

McCormick said that the damage could have been caused by a vessel, a dragging anchor or a big load that collided with the anchor cable, which is located near the west passage under the bridge, which is commonly used by water traffic on Lake Washington.

The broken cable is on the north side of the bridge, close to where construction crews currently are building the replacement for the 520 Bridge. However, state officials said that there is plenty of barge traffic on Lake Washington that could have caused the damage and they have not determined what vessel struck the cable. 

State officials said they are working with the U.S. Coast Guard to determine what happened, and they plan to file a report.

Rick Rodda, Assistant Bridge Maintenance Supervisor of Washington State Department of Transportation bridge maintenance, said that the cable was fine when last observed by state crews two or three weeks ago, which narrows the window of time that the cable could have been struck to the past month.

Dave Becher, WSDOT SR 520 floating bridge construction engineering manager, said the repair is expected to cost $200,000 or less. 

Crews can repair the bridge without closing it to traffic, according to WSDOT. The bridge was never closed due to the damaged anchor cable. The state said there are 58 anchor cables on the bridge, and that they would have closed the bridge if there had been sustained high winds of 30 mph.

Crews must dive to the lake floor to attach the cable to the anchor embedded in Lake Washington. The fix expected to be complete by Friday night, or Saturday at the latest, according to the WSDOT officials. 

Construction crews from the new bridge, Kiewit/General/Manson (KGM), are conducting the repairs since the group already has crews and necessary construction equipment on Lake Washington next to the damaged cable, according to the state.

KGM is working on the replacement of the State Route 520 floating bridge, with new construction visible just to the north of the existing span. The target date for opening is late 2014 or the first half of 2015, according to the state.